C. B12 Deficiency (Subacute combined degeneration)
1. Characteristics
- Subacute combined degeneration of the spinal cord results from deficiency
of vitamin B12. The mechanism of action is unclear, but this disorder is
associated with defective B12 absorption due to pernicious anemia. The primary
lesion appears to be in myelin.
a. Clinical Signs:
- 1) loss of position sense and other sensory deficits (due to posterior
column lesions)
2) lower extremity weakness, spasticity, increased deep tendon reflexes,
Babinski signs (due to corticospinal tract lesions)
- b. Location of Lesions: symmetrical degeneration of
- 1) posterior columns of spinal cord (affected first)
2) lateral columns of spinal cord
3) white matter of brainstem, optic nerves, cerebrum
- c. Pathological Characteristics:
- 1) diffuse, spongy degeneration of white matter
2) myelin and axonal degeneration
3) macrophage response & gliosis, particularly in treated cases